The objective of this proposal is to determine the extent and mechanism of the mediation of adenosine and adenine nucleotide effects by cyclic AMP in mammalian cells. An attempt will be made to determine whether adenosine and/or the nucleotides are physiological hormone or transmitter like compounds. The adenosine effects will be examined with reference to synergism or inhibition when alone or in combination with other hormones, such as the catecholamines, prostaglandins, and histamine. These effects on cAMP will be studied mainly in cells in tissue culture: to include both established cell lines, and primary cultures of brain cells, peripheral nerve cells, skin epithelia, fibroblasts, liver, capillaries, and heart cells. Effects will also be looked for in non- cultured systems; e.g., brain slices, blocks of peripheral nerve tissue, the isolated perfused liver, and isolated skin epithelia. A detailed investigation of the adenosine action on cAMP turnover and its effects on phosphodiesterase and adenyl cyclase, especially in the cultured brain astrocytoma cells will be undertaken. An effort will be made to determine if adenosine or the nucleotides are released and if so, by what stimuli, and whether once released, if they affect the cAMP system. Purine analogues of the adenine compounds will be examined for their effects on cAMP accumulation, as well as the known inhibitors of adenosine action on cAMP levels such as the methylxanthines.